In general, when duets that require a predetermined inner diameter, such as blood vessels, the esophagus, the pancreatic duct, or the bile duct, are constricted due to various reasons such as deposits or when there is a need for an operation, a stent that can artificially expand the constricted portion is inserted.
The circumferential parts of a stent need to be smoothly constricted and expanded in order to be easily inserted into a duct. To this end, stents are made of twisting a plurality of wires or a plurality of holes are formed through stents by a laser pattern. Accordingly, when a stent is inserted into a constricted portion, the tissues of the constricted portion protrude into the stent through the holes by pressure due to expansion of the stent. In particular, when a stent is installed in a duct for a long period of time or when the pressure due to expansion of a stent increased over a predetermined level, side effects such as injury or necrosis of the tissues of the narrowed portion may be generated.
Accordingly, various methods for solving these problems have been proposed. A method of forming a membrane to close the holes of a stent is representative of the methods.
A plurality of wires is twisted to form a stent, so a plurality of rectangular holes is formed through the surface. Further, the entire stent is coated with silicon etc. to close the holes in order to prevent the tissues of the installation portion from protruding into the stent. Accordingly, the stent can be stably fixed at the port ion and it is possible to prevent the tissues from protruding into the stent.
As described above, in order to close the holes of a stent, generally, there is a method of dipping a stent in liquid-state silicon or a method of manufacturing a film of silicon or polyurethane, covering a stent with the film, and then fixing both ends of the film to the stent using a suture.
However, according to the method of using dipping, a stent is entirely covered with silicon, so when the stent is inserted into a curved portion such as a digestive system, a strong restoring force for returning to the initial state acts. That is, the stent is not sufficiently flexible, so it may cause inflammation by generating friction on the diseased part.
According to the method of using a film, it is required to go through an additional biological test to obtain medical sanction on sutures, in addition to the stent, and there is a need for the additional process of fixing a film to the stent using a suture, it takes more costs and time to manufacture the stent.
Further, when a stent is entirely covered by the method of using dipping or a film, body fluid such as blood or pancreatin can smoothly flow inside the stent, but the body fluid flowing into a duct through a divergent duct such as intrahepatic bile ducts or pancreatic ducts cannot smoothly flow.
In order to solve these problems, a method of partially close the holes of a stent has been proposed, but the problem that tissues protrude into the stent through the holes still remains.